The present invention relates, in general, to semiconductor devices, and more particularly, to semiconductor device packages.
Semiconductor device manufacturers are constantly striving to lower the cost of manufacturing semiconductor devices while improving device electrical and thermal performance characteristics. In addition, it is desirable for the devices to be small, light weight, and have a low profile. Thus, over-molded pad array carrier (OMPAC) semiconductor devices have been developed to improve both the electrical and thermal performance of surface mount semiconductor devices. Typically, OMPAC semiconductor devices include a thin printed circuit board (PCB) substrate on which a semiconductor chip is mounted. Portions of the chip are electrically coupled to conductive traces formed on a top surface of the PCB. Each conductive trace is routed to a corresponding conductive trace on the bottom surface of the PCB by a conductive via which extends through the PCB. The traces on the bottom surface of the PCB each terminate at a conductive pad to form an array of pads on the bottom of the PCB. The semiconductor chip and a portion of the PCB are encapsulated by a molding compound using conventional molding techniques, i.e., placing the PCB having the semiconductor chip mounted thereon in a mold cavity, converting a mold compound from a pellet form to a liquid form, injecting the liquid mold compound into the mold cavity, and curing the mold compound. Although OMPAC semiconductor devices offer the advantages of increased interconnect packaging densities, elimination of coplanarity and skew limitations, low lead inductance, and a low profile, they require a different mold for each type of OMPAC semiconductor device. Since these molds are expensive, manufacturing different types of semiconductor devices is also expensive. In addition, the cost of maintaining molding equipment is high. Further, the mold compounds used in manufacturing OMPAC semiconductor devices require extensive cure times which result in increased cycle times.
Another type of surface mount semiconductor device is a glob-top pad array carrier (GTPAC) semiconductor device. A GTPAC semiconductor device comprises a PCB having a semiconductor chip mounted thereon and a wall or dam of thixotropic material formed on the PCB. The dam surrounds and is spaced apart from the semiconductor chip. Subsequently, the semiconductor chip and the portion of the PCB within the dam are covered by a liquid encapsulant. The dam and the encapsulant form a package body. Although, GTPAC semiconductor packages may offer an increased electrical performance over conventional surface mount packages, they require a thicker PCB to preclude planarity limitations. In addition, the dam material is difficult to dispense and increases cycle time, resulting in higher manufacturing costs.
Accordingly, it would be advantageous to have a method and a means for encapsulating semiconductor chips that does not limit the thickness of the PCB and is readily incorporated into existing manufacturing processes. It would be of further advantage for the method and means to reduce the cost and time required to manufacture semiconductor devices. In addition, it would be advantageous for the method and means to improve the electrical and thermal performance of the semiconductor device.